ROADSIDE REVEGETATION

An Integrated Approach to Establishing Native Plants and Pollinator Habitat

3.6 Gathering Field Information

Surveying reference sites, as well as the project area in general, for soils, climate, and vegetation will provide baseline ecological data for developing the revegetation plan. If creating pollinator habitat is a revegetation objective, then reference sites and the project area are also surveyed to assess pollinator habitat quality and pollinator populations. This survey will provide insight into which pollinator species might be supported or enhanced by the revegetation project. The goal of the field survey is to obtain sufficient information from reference sites to realistically define DFC targets. During an initial survey, the appropriate survey intensity can be determined based on information needs and knowledge gaps. For example, if one of the revegetation objectives is to restore an abandoned road to a DFC target similar to a neighboring forest, then a survey of vegetation and soils of an undisturbed and disturbed neighboring forest would be conducted to describe the site characteristics and species composition.

The data used to define revegetation units (Section 3.3) should be reviewed prior to the field surveying of reference sites. Information regarding land ownership, site history, resources, and past and current management is also valuable. Specialists who might have knowledge of the soils, vegetation, climate, and hydrology, as well as locals who can provide information on the site's history, should be contacted.

3.6.1 Vegetation Assessment

The objective of assessing the vegetation of a reference site is to create a comprehensive species list that will guide in the selection of species to be used for revegetating the project area. A good method for compiling a comprehensive species list is to choose a representative cross section of each reference site that will characterize the range of plant species for that unit. Intuitively controlled surveys, such as these, maximize floristic knowledge yet are less time and effort intensive than complete floristic inventories. Usually, a few plant species are not easily identified in the field. Samples of these species can be brought back to the office for identification by specialists. If more detailed data collection is desired, such as a complete floristic inventory, surveys along transects or grids may be conducted.

Once species are identified, a comprehensive species list is developed for the project (Table 3-6). This list will be used throughout the life of the project for selecting species for plant propagation, weed control, and plant protection. It includes some or all of the following attributes:

Table 3-6 | A comprehensive species list

Upon completion of a vegetation survey of the reference sites, a comprehensive species list is developed for the project. The spreadsheet will be used to determine the plant species mix that will be used in each revegetation unit.

Scientific name

Common name

Revegtation unit

Amplitude

Abundance

Life form

Nativity

Weed status

Threatened & endangered

Succession

Ecological setting

Pollinator friendly

Achillea millefolium

Common yarrow

2,3

High

High

Perennial Forb

Native

-

-

Early

All

Yes

Abies grandis

Grand fir

1

High

High

Tree

Native

-

-

Late

All

No

Abies lasiocarpa

Subalpine fir

1

High

Mod

Tree

Native

-

-

Late

Cool

No

Agastache urticifolia

Horsemint

2,3

High

High

Perennial Forb

Native

-

-

Early

All

Yes

Agoseris aurantiaca

Orange agoseris

2,3

High

Mod

Perennial Forb

Native

-

-

Early

All

Yes

Agoseris glauca

Pale agoseris

2,3

High

Mod

Perennial Forb

Native

-

-

Early

All

Yes

Agoseris grandiflora

Bigflower agoseris

2,3

High

Mod

Perennial Forb

Native

-

-

Early

All

Yes

Allium acuminatum

Tapertip onion

4

Low

Low

Perennial Forb

Early

-

-

Early

Wet

?

Allium fibriatum

Fringed onion

4

Low

Low

Perennial Forb

Native

-

-

Early

Warm/Dry

?

Allium macrum

Rock onion

4

Low

Low

Perennial Forb

Native

-

-

Early

Wet

?

Allium madidum

Swamp onion

4

Low

Mod

Perennial Forb

Native

-

-

Early

Wet

?

  • Species name (common and scientific)—Because common names for plant species change throughout the country, it is important to list both the scientific and common names of each species. The USDA PLANTS database is a good source for obtaining the current scientific and common names. The database also includes the short species code symbol for field documentation.
  • Revegetation unit—Identify the revegetation units where the species occurred.
  • Ecological settings—Plants are identified by the ecological setting they are most commonly found in. A relative rating by temperature (cold, cool, warm, hot) and moisture (dry, moist, wet) gives a quick profile of the ecological setting. Some portions of the U.S. are covered by plant association maps or reports that were developed by federal agencies and are good sources for identifying the ecological setting of a species. Another way to describe the ecological setting of a species is by using the Ecological Site Assessment section of the Web Soil website (Section 3.3.2). This part of the website groups soil mapping units into ecological site units and dominant plant species.
  • Amplitude—Ecological amplitude is the recurrence of a species across a wide array of ecological settings. A species found in all ecological settings would have a high ecological amplitude, while a species found in only one ecological setting would have a low ecological amplitude.
  • Abundance—The quantity, dominance, or cover of a species found in a revegetation unit is the abundance.
  • Life form—Group each species by life form: (1) tree, (2) shrub, (3) annual grass, (4) perennial grass, (5) annual forb, (6) perennial forb, or (7) wetland species (e.g., sedges, rushes)
  • Nativity—Identify whether the species is native to the local area or introduced. The USDA PLANTS database identifies the nativity of all plant species in the U.S.
  • Weed status—The USDA PLANTS database identifies the noxious weeds for each state. State-listed noxious weeds are found under the heading "Introduced, Invasive, and Noxious Plants" under the "PLANTS Topics" sidebar. Contacting the local State agency in charge of maintaining the lists, usually state departments of agriculture, is recommended.
  • Threatened and endangered species—State and federal protected plants are found in the USDA PLANTS database under the heading "Threatened & Endangered" on the "PLANTS Topics" sidebar.
  • Succession—Determine the seral stage a species is most commonly associated with: (1) early, (2) mid, (3) late, or (4) climax. Visiting reference sites and adjacent areas at different ages of recovery following disturbance will help provide an understanding of where each species fits into ecological succession. Figure 3-9 illustrates how plant communities develop differently over time depending on site conditions and successional processes.
  • Pollinator friendly—Reference the ERA to determine if a species is beneficial to pollinators. Use the ERA lists of pollinators associated with each plant species to build a highly diverse pollinator community; flower color is also helpful in this regard—the more the merrier. Flowering periods for plant species can be obtained from the ERA. Use these to maximize the seasons flowers are available to pollinators; a good minimum rule is three to five different species each of early, mid, and late bloomers. In addition to the ERA, other sources of reliable information such as species distribution maps by county from the USDA PLANTS website, or the I-35 Corridor plants list can give more detailed guidance to selection of appropriate species.

3.6.2 Soils Assessment

Understanding the soil characteristics of each reference site is essential to effectively define DFC targets and develop revegetation treatments. The soils report that is generated from the Web Soil Survey website for a road project gives a close approximation of the characteristics of undisturbed soils for the project area and should be checked in the field. It is important to remember that the soil condition after road construction will not resemble the natural soils found in the soil survey. For this reason, it is important to find disturbed reference sites that are similar to the disturbance of the revegetation unit. The following information can be collected for topsoil and subsoil:

  • Soil texture
  • Rock fragments
  • Rooting depth
  • Topsoil depth
  • Nutrient levels
  • Soil structure
  • Litter and duff layers (Section 5.2.3, see Litter and Duff)
  • Site organic matter
  • Infiltration rates

3.6.3 Pollinator Assessment

Habitat Assessment

During the field review, an assessment of the pollinator habitat and pollinator species populations may be conducted for the project area. The pollinator habitat assessment includes evaluating the road project plans within the context of the larger planning area for creating habitat supportive for general and at-risk pollinator species.Table 3-7 is a checklist that can be used to identify those factors important for creating pollinator-friendly habitat. Factors that improve pollinator health or habitat can be considered in design plans while factors that limit pollinator health can be mitigated or improved through management treatments or practices, presented in Section 3.9.

Table 3-7 | Pollinator habitat assessment checklist

This guide can be used to assess the pollinator habitat conditions at any time during the life span of a road project. The checklist gives eight characteristics important for most pollinator habitats, however, the designer may want to modify the checklist so that it addresses the climate, soils, vegetation, and pollinator species of interest specific to the project area and project objectives. It is important when using the checklist to identify the purpose of the assessment, such as whether it is describing a reference site, pre-disturbance or post-revegetation conditions.

Components of pollinator habitat

Steps to improve pollinator habitat conditions

Nectar/Pollen sources

  • At least three blooming species in each season (spring, summer, fall)
  • Species have overlapping and sequential bloom periods
  • Presence of both wildflowers and woody blooming plants
  • Aim for 45 percent plant cover of blooming plants available across seasons

Breeding habitat

  • Host plants present for target butterfly and moth species
  • Presence of vegetation, leaf litter that can serve as egg-laying sites for other species. At least three blooming species in each season (spring, summer, fall)

Nesting habitat

  • Patches of bare ground present at site
  • At least three species of woody plants or pithy stemmed plants that support tunnel-nesting bees
  • Snags or downed wood present in safe location for traveling public
  • Unmown bunch grasses present throughout growing season to support bumble bee nests

Water source

  • Water sources such as culvert outlets, ditches, draws, gullies, intermittent streams, and topographic enhancements

Shelter and overwintering

  • Trees and/or shrubs present at the site
  • Diversity of grasses to provide vegetation structure

Vegetation management

  • Mowing and herbicide use is timed to reduce impact to pollinator life cycles
  • Mowing and herbicide use is timed to support plant diversity
  • Herbicide use in roadside beyond the safety strip is targeted to noxious and nonnative plants and other undesirable species rather than using broadcast applications
  • Weeds are controlled before and during construction to aid in plant establishment, as well as during the establishment phase
  • If haying (mowing and removal of biomass) by adjacent landowners is permitted on the roadside, it is conducted once at the end of the growing season
  • Prescribed fire and prescribed grazing are timed carefully to avoid damage to life cycles of imperiled or sensitive species of pollinators
  • Brush removal is tapered to soften transition to denser vegetation at edge of ROW, opening up the canopy to allow understory plants to bloom and leaving some stems or other sites for tunnel-nesting bees
  • Biological and cultural control methods are integrated into vegetation management to reduce use of herbicides to control noxious and invasive weeds

Landscape connectivity

  • Site increases landscape connectivity by linking existing habitat parcels on nearby land
  • Site increases roadside connectivity by linking roadside habitat
  • Site increases diversity within the landscape and benefits agricultural activity on adjacent lands

Road mortality

  • Site is not isolated within areas of high road density in which there are multiple barriers to pollinator movement
  • Sites have reduced mowing and high plant diversity
  • Clear zone width is increased within AASHTO guidelines along roadsides with high salt use and high volumes of traffic (reduces exposure of pollinators to salts, heavy metals)

One approach to using this checklist is for the designer to visit the project site during planning and evaluate both the current condition of the roadsides and the undisturbed reference sites (Section 3.5). Ideally these assessments can be conducted during the same visits as the vegetation assessment (Section 3.6.1) and the soil assessment (Section 3.6.2). Evaluating the quality of pollinator habitat of the existing roadsides will give some indication of what the designer can expect if standard construction practices are employed. Comparing these findings to those of undisturbed reference sites gives the designer an idea of what is possible. Comparisons of the current condition and the reference site can help the designer develop a revegetation plan for improving pollinator habitat.

The Pollinator Habitat Assessment checklist provides eight characteristics important for most pollinator habitats. The designer may want to modify the checklist based on project objectives, pollinators of interest, and the unique ecology of the roadside. Another valuable use of the checklist is that it can be used to develop target DFCs for the revegetation project (Section 3.7). For example, a DFC target from this list may state that "at least three native species will be in bloom during spring, summer, and fall". Field visits during the growing season would be conducted after revegetation to determine if this target was met.

Pollinator Monitoring

Revegetation projects, especially those specific to improving pollinator habitat, may require a pre- and post-construction assessment of pollinator species. As discussed earlier, it may be helpful to know which pollinators are present prior to project design. If imperiled pollinator species are suspected in the project area, it is important to survey for pollinators before undertaking construction. See Section 3.3.4 for resources for determining imperiled pollinators in the project area and check with the state Natural Heritage Program and land managing agency, as applicable, for a list of species of conservation concern.

It can also be helpful to monitor pollinators before construction and following revegetation in order to assess the success of the project or to perform comparisons of the effectiveness of seed mixes or revegetation techniques for different pollinators. Monitoring techniques for these assessments are discussed in Section 6.4.